The present invention generally relates to inkjet and other types of printers and more particularly to a novel printing system that includes a system and method for controlling the thermal characteristics of an inkjet printhead.
Inkjet printers are commonplace in the computer field. These printers are described by W. J. Lloyd and H. T. Taub in xe2x80x9cInk Jet Devices,xe2x80x9d Chapter 13 of Output Hardcopy Devices (Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988) and U.S. Pat. Nos. 4,490,728 and 4,313,684). Inkjet printers produce high quality print, are compact and portable, and print quickly and quietly because only ink strikes a printing medium, such as paper.
An inkjet printer produces a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes xe2x80x9cdot locationsxe2x80x9d, xe2x80x9cdot positionsxe2x80x9d, or xe2x80x9cpixelsxe2x80x9d. Thus, the printing operation can be viewed as the filling of a pattern of dot locations with dots of ink. Inkjet printers print dots by ejecting very small drops of ink onto the print medium and typically include a movable carriage that supports one or more print cartridges each having a printhead with ink ejecting nozzles. The carriage traverses over the surface of the print medium. An ink supply, such as an ink reservoir, supplies ink to the nozzles. The nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller. The timing of the application of the ink drops typically corresponds to the pattern of pixels of the image being printed.
In general, the small drops of ink are ejected from the nozzles through orifices or nozzles by rapidly heating a small volume of ink located in vaporization chambers with small electric heaters, such as small thin film resistors. The small thin film resistors are usually located adjacent the vaporization chambers. Heating the ink causes the ink to vaporize and be ejected from the orifices.
Specifically, for one dot of ink, a remote printhead controller, which is usually located as part of the processing electronics of the printer, activates an electrical current from an external power supply. The electrical current is passed through a selected thin film resistor of a selected vaporization chamber. The resistor is then heated for superheating a thin layer of ink located within the selected vaporization chamber, causing explosive vaporization, and , consequently, a droplet of ink is ejected through an associated orifice of the printhead.
However, in typical inkjet printers, as each droplet of ink is ejected from the printhead, some of the heat used to vaporize the ink driving the droplet is retained within the printhead and for high flow rates, fluidic friction can heat the ink near the substrate. These actions can overheat the printhead, which can degrade print quality, cause the nozzles to misfire, or can cause the printhead to stop firing completely. Printhead overheating compromises the inkjet printing process and limits high throughput printing. Consequently, to avoid these problems it is important that the temperature of the printhead be maintained at a desired optimum temperature range. Current inkjet printheads, however, lack the capability of providing efficient localized thermal control at the printhead level because they are controlled by remote devices.
Therefore, what is needed is a new printing system and protocol that utilizes a printhead with an integrated distributive processor having a thermal controlling for providing efficient control of the thermal characteristics of the printhead.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention is embodied in a novel printing system and protocol including a printhead with an integrated distributive processor having a thermal controller that provides efficient and localized control of the thermal characteristics of the printhead. The present invention regulates printhead temperature within a desired optimum range and reduces problems associated with the printhead temperature being outside of the optimum range. Moreover, the present invention provides localized control over these thermal characteristics, thereby increasing the efficiency of the printhead.
The printing system includes a controller, a power supply and a printhead assembly having a memory device and a distributive processor integrated with an ink driver head. The distributive processor includes a thermal controller for determining the printhead temperature, providing feedback to control devices including the distributive processor and making control decisions based upon measured thermal characteristics of the printhead.